The 2018 elections will test whether Democrats can break the Republican stronghold on statewide offices and the Legislature.

But first, Republicans are going through their biennial family fight, with numerous primary contests for Texas House and critical races for North Texas Senate seats.

Filing for the party primaries closed at 6 p.m. Monday, but the full picture of some races may not be known immediately because it could take a day or two for the Texas secretary of state to update the list of official candidates.

This much is certain: The Dallas area will see at least three new members of Congress as contenders battle to fill the seats of retiring Republicans Sam Johnson, Jeb Hensarling and Joe Barton.

"At the end of 2018, the state will look very similar to how it does now. We'll still be a red state where Republicans are dominant," said Rice University political scientist Mark Jones.

But Jones said the state's congressional races against Republican incumbents Pete Sessions in the Dallas-area 32nd District, John Culberson in Houston's 7th District and Will Hurd in South Texas' 23rd District proves Democrats can field credible challengers.

"The optimism for Democrats will be in some of these congressional races," Jones said.

Nearly all of the statewide Republican office holders have little or no opposition in the GOP primary. The exception is incumbent Land Commissioner George P. Bush, who faces a significant challenge from the man he succeeded on the job, Jerry Patterson.

Gov. Greg Abbott and Lt. Gov. Dan Patrick will cruise to primary victories. Attorney General Ken Paxton, who is battling security fraud charges, didn't draw a challenger -- an indication that his party doesn't see him as a political liability.

Sen. Ted Cruz, with Gov. Greg Abbott during a campaign event in Houston in 2016, faces opposition in the GOP primary.

(File Photo/The New York Times)

Sen. Ted Cruz faces opposition in the GOP primary including Bruce Jacobson Jr., a Christian television show producer and former Ronald Reagan adviser from North Richland Hills.

While the state's top Republican leaders won't see major opposition in their primaries, Democrats have fielded a full slate of statewide contenders, including candidates for governor and senator.

Democrats will have a primary contest to determine whether Dallas County Sheriff Lupe Valdez, Houston investor Andrew White or someone else earns a ticket to the general election contest against Abbott.

Lupe Valdez was greeted by well-wishers after announcing her candidacy last week in the Texas governor's race.

(Louis DeLuca/Staff Photographer)

Meanwhile, Rep. Beto O'Rourke, D-El Paso, has emerged as the Democrats' most exciting candidate on the ticket, though he still faces an uphill battle against Cruz.

Congress

The state's in-district battles could be the most hard-fought.

Hotly contested GOP and Democratic Party primaries are on tap to replace Barton in the 6th Congressional District 6 and Hensarling in the 5th District. In Collin County's 3rd Congressional District, state Sen. Van Taylor is poised to win that GOP primary, which is tantamount to winning the seat outright.

In the 5th, the leading contenders to replace Hensarling are state Rep. Lance Gooden, R-Terrell, Garland Republican Bunni Pounds and former state Rep. Kenneth Sheets of Dallas.

The most-watched congressional contest is in the 32nd District, where numerous Democratic contenders are vying to challenge incumbent Republican Sessions. They include former Hillary Clinton adviser Ed Meier, former Housing Department special assistant Colin Allred, former Department of Agriculture official Lillian Salerno and former WFAA-TV (Channel 8) television reporter Brett Shipp.

Legislature

Primary battles are the focus of several North Texas Senate races.

One of the most anticipated contests is in Senate District 8, where McKinney educator Angela Paxton is running against Richardson businessman Phillip Huffines. Paxton is the wife of Ken Paxton, the attorney general, and Huffines is the twin brother of state Sen. Don Huffines.

In Senate District 2, state Rep. Cindy Burkett of Sunnyvale is challenging incumbent Republican Bob Hall of Edgewood. And in District 30, state Rep. Pat Fallon of Frisco is mounting a GOP primary challenge against Craig Estes of Wichita Falls.

Republican incumbents in the House across the state are facing numerous challenges. But the key question is how many seats Democrats can pick up in 2018.

The answer to that question lies in Dallas County, where Democrats have candidates in most districts with Republican incumbents, and the GOP is trying to unseat Democratic incumbent Victoria Neave, D-Dallas.

Local contests

The race for Dallas County district attorney is set. Former state District Judges John Creuzot and Elizabeth Frizell will have a March 6 Democratic primary battle for the chance to unseat Republican incumbent Faith Johnson.

And the Democratic Party race to succeed Valdez so far is a three-way battle among Chief Deputy Marian Brown, Dallas County Constable Roger Williams and Dallas lawyer Pete Schulte. The filing period for that race ends Dec. 16.